There is a current tendency to manufacture new models of wind turbines capable of generating more power, which thus tends to increase the dimensions of their rotors by the enlarging of their blades.
As known in the state of the art, wind turbine blades comprise a beam with a longitudinal extension, which represents the structural element of the blade, covered with an external skin known as shells, an upper and lower, manufactured using molds known as shell molds.
These shell molds are primarily made of composite fiber materials and resins, with certain metal structural and are utilized to shape the piece, cure materials in the blade and assemble them to obtain the final product, i.e., the wind turbine blade.
Manufacturing was traditionally carried out in two parts, upper and lower, that correspond with the two external skins of the blade. In other words, two semi-molds that are set up to form a single piece based on the geometry of the blade intended to be obtained from the base model.
Shell semi-molds are large-dimensioned elements that are generally rectangular in form and interconnected with some actuators that work as hinges, hence opening and closing the shells. Fabrics of composite material are laid on each of the semi-molds to conform, on each one, with a part of the blade. To do so, once the fabrics have been laid, the mold is closed thereby initiating curing or heating of the mold, positioning the part of the mold corresponding to the hub together with the air injection system and, consequently, the part corresponding to the blade tip towards the free part of the mold.
An example of the shell mold is described in Spanish patent ES2208028, which is primarily formed by non-metallic materials, a composite material bed, a metal structure and composite sandwich panels that provide support to the bed and serve for air conduction, a mechanical system that moves one of the two semi-molds for carrying out opening and closing operations, and a heating system that allows the mold to function as an oven. The system is in turn equipped with is self-supporting structural air conduits forming the sandwich panels and are supported longitudinally by some metal ribs. The mold structure affords a certain degree of liberty vis-à-vis the driving system, by sliders located in the metal ribs and joined together when opening or closing so as to enable expansion without undergoing stress while it undergoes heating.
The aforementioned increase in rotor dimensions and the ensuing lengthening of blades result in the need to produce a shell mold for each new blade geometry intended for production. This implies substantial manufacturing costs, not only for the cost of the mold itself, but also for the time elapsed for the full process.
Solutions known in the State of the art suggesting the production of blades by parts, such as the one described in international patent WO2009/156061, in order to standardize the blade production process. To do so, a method is employed according to which the different parts of the blade are manufactured independently and subsequently joined together using an integration device. However, this solution focuses on the production of a standard blade and calls for, if production of blades differing in geometry from the standard blades is required, an integration device for this specific blade geometry. Further, the method described therein could generate difficulties in obtaining a quality final product, since it could present irregularities or weak points at the surfaces of the joint areas for the different parts of the blades, which will thus condition their behavior.